In order to power certain electronic devices, in particular those intended for aeronautics, it sometimes proves to be necessary to generate electric voltages of high level, from a low-voltage common supply generator. The “boost converters” used for this purpose are chopper converters that are nonisolated so as to retain high efficiencies and small dimensions.
FIG. 1a shows a basic diagram of a voltage booster converter of the prior art.
The circuit of FIG. 1a is powered, via two input terminals A and B, by a generator E of DC input voltage Vin and provides a DC output voltage Vout on a load Rout in parallel with a capacitor Cout. The positive pole of the generator E is connected, across an inductor Lin and a diode Dd, to a terminal C of the resistor Rout in parallel with the capacitor Cout, the other terminal D of the resistor Rout being connected to the negative pole of the generator E. A switch Int connected, on the one hand, to the connection point of the inductor Lin and the diode Dd, and, on the other hand, to the negative pole of the generator E, periodically places the inductor Lin in parallel with the generator E.
The switch Int is turned on for the time Ton and open for the time Toff. The diode Dd is conducting for the time Toff and open for the time Ton. We refer to α=Ton/(Ton+Toff) as the duty ratio.
FIG. 1b shows the control signal of the switch Int of the “boost converter”.
When Int is closed, for the time Ton, the inductor Lin sees at its terminals the voltage Vin of the generator E. The current ILin in this inductor increases by the value:ΔILinTon=Vin.Ton/Lin
When the switch Int is open and the diode Dd conducts, that is to say for the time Toff, the inductor Lin sees at its terminals the difference between the input voltage Vin and the output voltage Vout. The current ILin in this inductor therefore decreases by the value:ΔILinToff=((Vin−Vout).Toff)/Lin
The equilibrium state is attained when the sum of these two variations is zero, i.e.:((Vin−Vout).Toff)/Lin +Vin.Ton/Lin=0
which leads to the expression for the equilibrium voltage:Vout=Vin/(1−α)
α lying between 0 and 1, the output voltage Vout is therefore higher than the input voltage Vin, the structure of FIG. 1a is that of a voltage booster.
FIG. 1c shows the current in the “boost converter” of FIG. 1a. 
In practice, the switch Int may advantageously be embodied by semiconductors. Mention may be made, in a nonlimiting manner, of MOS and bipolar transistors, IGBTs or MCTs.
The voltage booster converters of the prior art comprise limitations. Specifically, it is difficult to obtain voltage ratios Vout/Vin of greater than 5 while retaining optimal converter efficiency. Specifically, the switch is subjected at one and the same time to very large currents and high voltages.
Other nonisolated structures may be used. Mention may for example be made of the autotransformer type boost converter or the placing of two boost converters in series. Unfortunately, none of these solutions exhibits the expected efficiency performance.